Since the introduction of electrical power distribution systems in the late 19th century, there has been a need to monitor their operational and electrical characteristics. The ability to collect, analyze, and respond to information from an electrical power system can improve safety, minimize equipment loss, decrease scrap, and ultimately save time and money. To that end, monitoring devices were developed to measure and report such information. With the dawn of the electronics age, the quality and quantity of data from monitoring devices was vastly improved, and communications networks and software were developed to collect, display, and store information.
All real-world electrical signals on power systems experience subtle changes in their frequency and amplitude over time. This modulation of the power signal's frequency and amplitude are both indeterminate and unique with respect to time. Each device located on the same electrical grid will simultaneously experience the same frequency fluctuations during steady-state load conditions. Devices that are directly linked to each other in their hierarchy will see stronger correlations in their amplitude modulation. Both the frequency and amplitude modulation of the signal may then be used to precisely synchronize the data from one device with respect to another device (or all devices to each other).
Currently, data synchronization features such as that described in U.S. Pat. No. 7,684,441, and U.S. Pat. No. 8,024,390, allow all devices on a monitoring system to be synchronized to the zero-crossing of all three phase voltages without the use of additional hardware. Potential phase shifts between various devices can also be detected with these systems. Once the devices are synchronized with each other, the system data is essentially synchronized with respect to the time it occurred making more complex data analysis feasible.
The need to synchronize data across different power monitoring systems or electrical grids is becoming more commonplace as the sophistication of electrical systems evolve. Synchronizing monitoring system data allows users to determine how an event propagates through their electrical system, how it affects equipment, and potentially how to mitigate reoccurrences. One example of monitoring equipment is the ProActiveLogic® technologies available from Schneider Electric, which provides more extensive data synchronization opportunities in applications (Data Centers, Islanding Systems, et al.) that heretofore required GPS timestamping (along with the associated GPS equipment, installation and configuration costs).
Sophisticated processing capabilities in digital monitoring devices allow large amounts of complex electrical data to be derived and accumulated from a seemingly simple electrical signal in individual utility systems. Because of the data's complexity, quantity, and ostensibly disjointed relationship from one monitoring device to the next (and one electrical grid to the next), manual analysis of all the data is an enormous effort that often requires experts to be hired to complete the task. This process is tedious, complicated, prone to error and oversight, and time-consuming. A partial solution has been to use global positioning satellite (GPS) systems to timestamp an event between different electrical grids, but this approach requires that the user purchase and install additional hardware and data lines to link the monitoring devices of different electrical grids together. And this solution still requires the evaluation of large amounts of data because the system data is only in temporal context; not in spatial context. Synchronizing data using GPS systems may be disadvantageous because of temporal latencies associated with other hardware in the system. Furthermore, any alignment of data by a GPS-based system can only be as accurate as the propagation delay of the GPS signal, which means that the data still may not be optimally aligned when a GPS system is used.
Systems that use large uninterrupted power supplies (UPS) such as data centers for example use multiple independent electrical “grids”; in this case the electrical utility grid and the “UPS grid.” Because these electrical grids are intentionally isolated from each other and move independently from each other (in the electrical sense), data synchronization using existing monitoring technologies such as the existing Schneider ProActiveLogic® technologies is impractical. What is needed, therefore, is a method to automatically and inexpensively perform precise data synchronization between multi-grid electrical systems.